The invention relate a method and a tool for stripping a cable, in particular a fiber ribbon cable.
A fiber ribbon comprises several optical fibers held together, for example, by a polymer jacket or sleeve. The fibers are located adjacent to each other, isolated from each other and from the environment, and are fixed in parallel to each other. The number of fibers that are located in parallel is of course optional. Commercially in, for instance, Sweden fiber ribbons having four parallel fibers, 4-fiber ribbons, are used, while in the U.S. 12-fiber ribbons are used. Also 6- and 8-fiber ribbons are today commercially available.
In splicing two different fibers, which usually is performed by fusioning or welding, the primary protective coating must first be removed. That is, both the individual protective coating of the fibers and the material that keeps the fibers together as a fiber ribbon, must be stripped. Thereupon the uncovered fibers are cut to then be welded to each other.
In order to strip the primary protective coating, the entire fiber ribbon is first heated, by for example, a fiber tool such as the tool described in Swedish patent application 9103492-6, filed Nov. 11, 1991. Heating is performed to soften the primary coating of the fiber ribbon, which in turn reduces the friction forces holding the coating to the fibers, thus facilitating the stripping operation. After heating, the primary protective coating is cut into by two blades having opposed edges, which pinch the long sides of the fiber ribbon about 35-50 mm from the end thereof, which is the length that usually must be removed. Then one pulls the fiber ribbon with two possible outcomes:
1. The primary protective coating is pulled away in the shape of a long thin plastic tube. PA1 2. The primary protective coating is scraped away as small particles.
The first of these two cases is the desirable one, because the second case results in many small particles which contaminate the stripping tool and work area requiring cleaning. Furthermore, the stripped fiber ends also become dirty, and then they too must be cleansed. Further, if the heated fiber ribbon is made too soft, i.e. too much heat is supplied, the result will be that the fiber ribbon is easily deformed and the primary protective coating is torn to pieces, which is also an undesirable result.
It is not very difficult to strip a fiber ribbon having relatively few fibers joined to each other, for example the 4-fiber ribbons commonly used in Sweden. This is due to the fact that a relatively small force is required for removing the relatively small amount of primary protective coating from the optical fibers in the shape of a long thin tube. Tools for accomplishing this are thus commercially available today, for example "ECC4", manufactured by the company Ericsson Cables AB.
Another stripping tool for optical fibers is described in the U.S. Pat. No. 4,188,841 which discloses a stripping tool for a single optical fiber. The tool may comprise a number of serially arranged pairs of blades, which are fixed in relation to each other, having the purpose of avoiding a repeated stripping process when stripping long coatings of an optical fiber.
The German published patent application No. 40 38 414 relates to a stripper apparatus for optical fibers, in which two blade systems are included, by means of which an outer coating and both an outer and inner coating respectively are penetrated in the stripping operation. In this manner a stripped fiber end is obtained, where the inner coating sticks out outside the outer coating.
When stripping fiber ribbons having a larger number of fibers, for example 12-fiber ribbons, presently used in the U.S.A., it is not equally simple to pull off the primary coating in the shape of an unbroken tube piece. The primary protective coating must be removed using a much larger force than that required for a 4-fiber ribbon. The result, when a tool similar to the aforementioned ECC4 is used, is often that the primary coating is torn to pieces.
Another problem which can occur is that the remaining plastics matrix of the ribbon fiber is deformed, so that the stripped fibers begin to point in different directions, which hinders the subsequent cutting and welding to a significant extent. In order to avoid these problems the fiber ribbon can be stripped in several stages of about 8-10 mm at a time. As a result, the force required for removing the primary protective coating becomes smaller and the coating can be removed as short tube pieces. However, the work of performing successive stripping operations for each 8-10 mm becomes cumbersome, since the length to be stripped usually is between 35 and 50 mm.